A contribution to the bad harvest on rice in Tôhoku District

Abstract

The about seventy successive years' statistics of rice production per unit area (=tan) is analysed by the least square method and picked up the bad harvest years that the ordinary harvest index=Ic is smaller than seventy five per cent in Tohoku district and its neighbours. The results are shown in table 1 and figure 1.From above result, the bad harvest on rice in Tohoku district are (1) transitional with the latitude parallel mainly, and (2) heavier in the Pacific Coast region than in the Japan Sea Coasts. But this tendency is opposite and slighter in the southern neighbour district generally.From the appearance of the hervest year as shown in figure 3, we may find the bad harvest years' group and the cyclic appearance of the bad harvest years.By the stochastical small sampling calculation on the bad harvest appearance, there are obtained (1) x=17.3 years and the confidence interval=11.0-23.6 years by α=0.05 case, or 13.1-21.5 years by α=0.10 case on the width of a bad harvest group, and (2) the result as shown in table 2, on a cyclic length of the bad harvest years' appearance.